CN104197714A - Piezoelectric ceramic sintering furnace with polarization function and sintering polarization method thereof - Google Patents

Abstract

The invention relates to the field of ceramic material manufacturing, in particular to a piezoelectric ceramic sintering furnace with the polarization function and a sintering polarization method of the piezoelectric ceramic sintering furnace. The piezoelectric ceramic sintering furnace comprises a furnace body composed of refractory bricks and further comprises a high-pressure polarization system. Multiple heating rods which are parallel up and down are arranged in the furnace body and penetrate into the refractory bricks. Two opposite plate electrodes are arranged close to the heating rods and embedded in the surfaces of the refractory bricks. A thermoelectric couple is formed between the two plate electrodes. A sample room composed of two transverse heat-resisting boards and two vertical refractory bricks is arranged between the two plate electrodes. The plate electrodes are connected with the high-pressure polarization system outside the furnace body through electrode leads. The high-pressure polarization system is used for controlling a polarized electric field of the plate electrodes. A temperature control system is used for controlling the temperature of the furnace body. The sintering process and the polarization process in the piezoelectric ceramic preparation technology are integrated, high-temperature polarization is conducted through remaining heat after sintering operation, so that energy consumption is reduced, and time is saved.

Description

Piezoelectric ceramic sintering furnace with polarization function and its sintering polarization method

technical field

The invention relates to the field of ceramic material manufacture, in particular to a piezoelectric ceramic sintering furnace with polarization function and a sintering polarization method thereof.

Background technique

Piezoelectric ceramics is a functional ceramic material that can convert mechanical energy and electrical energy into each other. It is a kind of functional ceramic material and also belongs to inorganic non-metallic materials. Piezoelectric ceramics are made by using their materials under the action of mechanical stress to cause the relative displacement of the internal positive and negative charge centers to cause polarization, resulting in the appearance of bound charges with opposite signs on the surface of the material, that is, the piezoelectric effect. It has sensitive characteristics. Ceramics are mainly used in the manufacture of ultrasonic transducers, underwater acoustic transducers, electroacoustic transducers, ceramic filters, ceramic transformers, ceramic discriminators, high voltage generators, infrared detectors, surface acoustic wave devices, electro-optic devices, In addition to being used in high-tech fields, ignition and detonation devices and piezoelectric gyroscopes serve people more in daily life.

At present, the existing manufacturing process of piezoelectric ceramics includes: batching - mixing and grinding - pre-firing - secondary grinding - granulation - molding - plastic discharge - sintering - electrode - high pressure Polarization-aging test.

The sintering process usually refers to the process of reducing the area of the powder-particle composite (bad body), reducing the porosity, increasing the density, increasing the contact area between particles, and improving the mechanical strength at high temperature. In addition to ordinary high-temperature sintering, there are also methods such as hot pressing sintering, hot isostatic pressing sintering, and plasma sintering.

The polarization process makes the internal electrical domains of the ceramics aligned, so that the ceramics have piezoelectric properties. The usual polarization process is to heat the piezoelectric ceramic sample in silicone oil to about 120 degrees, apply a DC electric field of 3.0kV/mm-5.0kV/mm between the electrodes, and maintain it for 15-20 minutes.

By the electrode process, the upper conductive electrode is set on the required ceramic surface. The general methods include silver layer burn-in, chemical deposition and vacuum coating. The technical requirements of chemical deposition and vacuum coating are relatively high, and the fire-infiltration technology of silver layer is relatively simple. At present, there are also methods of using aluminum (patent No. 200910192539) or tin (patent No. CN 200610031852) to replace silver, and non-burning silver paste, which can avoid The process of burning silver.

The disadvantage of the prior art is that the sintering process and the polarization process are separated, and after the sintering is completed, the residual temperature in the sintering furnace is not used, which is a waste of energy consumption. In addition, if the high-temperature polarization method is performed after the piezoelectric ceramics are sintered, it needs to be reheated to near the Curie temperature, which wastes electric energy and time.

Contents of the invention

Aiming at the deficiencies in the prior art, the invention provides a piezoelectric ceramic sintering furnace with polarization function and a sintering polarization method thereof.

The invention adopts the principle of high-temperature polarization, and when the piezoelectric ceramics cool down to the Curie point, a paraelectric-ferroelectric phase transition occurs and spontaneous polarization occurs simultaneously. The high-temperature polarization method is to add an electric field before the ferroelectric phase is formed, so that the paraelectric-ferroelectric phase transition is carried out under the action of an external directional electric field, and the electric domain has a higher preferred orientation as soon as it appears. In addition, at high temperature, the c/a axis of the ferroelectric phase is relatively small, and the electric domain does not suffer much resistance when it turns 90 degrees, and the domain wall moves easily, so as long as the electric field is very low, a high electric field at low temperature can be obtained the polarization effect. The electric domain: a part of the crystal that has the property of spontaneous polarization and has the same spontaneous orientation, these regions are called electric domains.

The technical scheme that the present invention takes is:

A piezoelectric ceramic sintering furnace with polarization function, which includes a furnace body made of refractory bricks and a high-voltage polarization system. Inside the furnace body are arranged a number of heating rods parallel to each other up and down, and the heating rods run through the refractory bricks. Inside; two opposite electrode plates are arranged close to the heating rod, the electrode plates are embedded on the surface of the refractory brick, and a thermocouple is formed between the two electrode plates; A sample room composed of two horizontal heat-resistant plates and two vertical refractory bricks; the electrode plate is connected to the high-voltage polarization system outside the furnace body through the electrode lead wire, and the high-voltage polarization system is used to control the polarity of the electrode plate Chemical electric field and control furnace body temperature.

The high-voltage polarization system includes a high-voltage polarization circuit, a temperature control circuit, a protection circuit and a time relay.

The sintering furnace disclosed by the invention can realize high-temperature polarization directly in the sintering furnace by using the residual temperature after the sintering is completed, and this process can be completed with a relatively low DC voltage.

On the basis of the above solution, the above and below parallel heating rods and the lower heating rods run through the interior of the refractory bricks.

On the basis of the above solution, the number of the upper heating rods is twice the number of the lower heating rods for the above-mentioned parallel heating rods.

Since the bottom of the furnace is used to place piezoelectric ceramic samples, the heating rods should not be exposed in the furnace, but should be placed in refractory bricks, while the upper heating rods can be exposed on the top of the furnace, and the heating effect is better, so the number of the upper part is usually the number of the lower part. 2 times to enhance the heating effect.

On the basis of the above solution, the electrode plate is a metal plate resistant to 1400°C, and the metal plate is coated with a protective layer of silver, gold or platinum.

On the basis of the above scheme, the fire-resistant plate is an alumina high-temperature heat-resistant plate.

The metal plate used in the present invention can be any metal plate resistant to 1400°C high temperature, such as copper, iron, etc., and the precious metal protective layer can be metals that cannot be oxidized at high temperatures such as silver, gold, platinum, etc., in the method of plating the protective layer On the surface, it can be a chemical film crossing method, or a physical film crossing method, such as magnetron sputtering, vacuum film crossing, etc.

Another object of the present invention is to disclose a method for sintering polarization of the above-mentioned piezoelectric ceramic sintering furnace, comprising the following steps:

(1) Sintering and high temperature polarization:

Put the piezoelectric ceramic sample into the sintering furnace according to claim 1, keep it warm at 1100°C-1400°C for 2-12 hours, then cool down to 1000°C at a constant speed of 3-8°C; 10-20°C above the internal temperature, start the polarization program, and take out the ceramic sample after polarizing the sample;

(2) By electrode:

After the piezoelectric ceramic sample is taken out, clean the upper and lower sides, apply the non-fired silver paste evenly on the upper and lower sides of the sample, and dry it at 150°C for 5-8 minutes. After the silver paste is dried, the piezoelectric performance test can be carried out.

On the basis of the above scheme, the polarization program in the sintering and high temperature polarization process is to first apply a DC electric field of 20-40V/mm, and control the temperature to drop at a rate of 5-10°C/min, while gradually increasing the polarization electric field, When the furnace temperature dropped to 100°C, the polarization electric field increased to 3000V/mm; after that, the temperature was naturally lowered to room temperature, the external electric field was removed, and the ceramic samples were taken out.

Among them, the Curie temperature refers to the temperature at which a material can change between a ferromagnet and a paramagnet, that is, the phase transition temperature at which a ferroelectric transforms from a ferroelectric phase to a paraelectric phase. It can also be said to be the transition temperature at which the second-order phase transition occurs. The Curie temperature of ceramics is generally between 200-500°C, and the Curie temperature of ceramics with different formulations is also different.

The beneficial effects of the present invention are:

The invention combines the sintering process and the polarization process in the piezoelectric ceramic preparation process into one, uses the residual temperature after sintering to perform high-temperature polarization, and saves energy consumption and time. The usual polarization process is carried out separately, and each piece of sample also needs to be carried out separately, and at the same time, it needs to go through the process of heating up, keeping warm and then cooling down, which lasts for a long time. However, in the present invention, the heating process can be omitted, and all ceramic samples can be polarized at the same time, saving energy consumption and time.

Description of drawings

Accompanying drawing 1 is the structural representation of sintering furnace of the present invention;

Accompanying drawing 2 is the basic schematic diagram of sintering furnace of the present invention;

Accompanying drawing 3 is the structural diagram of high-voltage polarization circuit of the present invention;

Accompanying drawing 4 is a schematic side view of the sintering furnace of the present invention along the central axis of the furnace body;

Accompanying drawing 5 is the schematic diagram of the structure of the sintering and polarization device in the sintering furnace of the present invention;

Accompanying drawing 6 is the setting linear diagram of polarization electric field in cooling process of the present invention;

Among them, (A) linear change, (B) nonlinear change;

1 is furnace body; 2 is heating rod; 3 is furnace space; 4 is electrode plate; 5 is thermocouple; 6 is heat-resistant plate; 7 is refractory brick; 8 is sample; 9 is high voltage polarization system; 10 is Heating power.

Detailed ways

The specific embodiment of the present invention is as follows: as shown in Figure 1-6,

A piezoelectric ceramic sintering furnace with polarization function, comprising a furnace body 1 made of refractory bricks, the space 3 in the furnace is rectangular, and a high-voltage polarization system, and a plurality of heating rods parallel up and down are arranged inside the furnace body 1 2. The lower heating rod runs through the interior of the refractory brick; two opposite electrode plates 4 are arranged close to the heating rod 2, and the electrode plates 4 are embedded on the surface of the refractory brick, and a thermoelectric power is formed between the two electrode plates 4. Couple 5; a sample room consisting of two horizontal aluminum oxide high-temperature heat-resistant plates 6 and two vertical refractory bricks 7 is set between the two electrode plates 4, and the piezoelectric ceramic samples 8 can be placed in groups of 4. In the sample room (as shown in Figures 4 and 5); the electrode plate 4 is connected to the high-voltage polarization system 9 outside the furnace body through the electrode lead wire, and the high-voltage polarization system 9 is used to control the polarization electric field of the electrode plate 4 and control The temperature in the furnace body, the heating power supply 10 of the sintering furnace is for heating the heating rod 2.

For the above and below parallel heating rods, the number of the upper heating rods 2 is twice the number of the lower heating rods.

The electrode plate 4 is a metal plate resistant to 1400° C., and the metal plate is coated with a protective layer of silver, gold or platinum. The metal plate used can be any metal plate that can withstand high temperatures of 1400°C, such as copper, iron, etc., and the precious metal protective layer can be silver, gold, platinum, etc. that cannot be oxidized at high temperatures. In the method of plating the protective layer, It can be chemical coating method (patent CN100335679 C, patent CN1375017 A), or physical coating method, such as magnetron sputtering (patent CN102084023 B), vacuum coating, etc.

Among them, the high-voltage polarization system includes a high-voltage polarization circuit, a temperature control circuit, a protection circuit and a time relay.

High-voltage polarization circuit: The function of the polarization high-voltage generating circuit is to provide suitable electric field conditions for polarization, which is a key part of the piezoelectric ceramic polarization device. The functional block diagram of the polarized high-voltage generating circuit is shown in Figure 3. In this circuit, the center-tapped voltage regulating transformer and step-up transformer are used to boost the mains voltage, and then output AC high voltage, which is then rectified by a bridge rectifier circuit to obtain polarized voltage. The required DC high voltage. During polarization operation, adjust the voltage regulating transformer slowly to increase the output DC voltage slowly, which can provide a suitable DC electric field for polarization.

Time relay: The relay is mainly used to set and control the polarization time, and the polarization time can be freely selected according to actual needs. Once the polarization time is up, it directly shuts off the high voltage generating circuit. Play the role of time control and protection.

Protection circuit: Add a fuse to the high-voltage polarization circuit to disconnect the polarization high-voltage circuit to protect it when the current is too large.

Temperature control circuit: The temperature control heating circuit is a general strong electric power supply and control circuit. The function is to provide certain temperature conditions for polarization. This part is equipped with "full pressure" and "voltage regulation" power supply and heating methods. The "full pressure" heating method refers to direct power supply and heating to the heater with AC 220V. "Voltage regulation" heating means that according to the needs of heat preservation when the polarization temperature and the ambient temperature maintain a fixed temperature difference, the voltage regulation circuit adjusts the appropriate voltage to supply power to the heater for heating. The voltage is displayed with a voltmeter. The temperature controller is used to set and control the oil temperature in the polarized oil tank, and the overtemperature and undertemperature information can be fed back to the voltage regulating circuit for adjustment to ensure the accuracy of the polarization temperature. Here, the DHC2T-D intelligent temperature controller is used to realize temperature measurement and control within 300°C, and it has the function of maintaining constant temperature, and can display the temperature through LED.

The method for sintering polarization in a piezoelectric ceramic sintering furnace comprises the following steps:

(1) Sintering and high temperature polarization:

Put the piezoelectric ceramic sample 8 into the furnace body 1 of the sintering furnace, keep it warm at 1100°C-1400°C for 2-12 hours, and then cool down to 1000°C at a constant speed of 3-8°C; then cool naturally to the Curie temperature of the piezoelectric ceramic When the temperature is 10-20°C above, start the polarization program, first apply a DC electric field of 20-40V/mm, and control the temperature to drop at a rate of 5-10°C/min, while gradually increasing the polarization electric field, when the furnace temperature drops to 100°C , the polarization electric field was increased to 3000V/mm; after that, the temperature was naturally cooled to room temperature, the external electric field was removed, and the ceramic sample was taken out.

The relationship between the polarization electric field and temperature during the polarization process is shown in Figure 6. During the high temperature polarization process, there are two schemes for the change of the polarization voltage, linear change and nonlinear change, as shown in Figure 6(A) and Fig. 6(B). Among them, the minimum polarization electric field intensity E _min =20-40V/mm, the maximum polarization electric field intensity E _max =3000V/mm, when the piezoelectric ceramics with high insulation performance can properly increase the polarization electric field intensity, on the contrary, the poor insulation performance Piezoelectric ceramics should properly reduce the polarization electric field strength. Different piezoelectric ceramics have different properties, and the polarization program is also different. The specific selection criteria should be based on the performance of the piezoelectric ceramics. The piezoelectric ceramics with good insulation can be selected (A) linear change, and the rate of change can be 5 ^o C/minute or so; Piezoelectric ceramics with poor insulation performance can be selected (B) Non-linear change, the change rate depends on the situation.

(2) Polarized:

After the piezoelectric ceramic sample is taken out, clean the upper and lower sides, apply the non-fired silver paste evenly on the upper and lower sides of the sample, and dry it at 150°C for 5-8 minutes. After the silver paste is dried, the piezoelectric performance test can be carried out.

Among them, the non-burning silver paste can be selected: Hunan Lide Electronic Paste Co., Ltd., medium temperature conductive silver paste DT550X.

Claims (7)

1. have a piezoelectric ceramics sintering furnace for function of polarization, comprise the body of heater (1) being made up of refractory brick, also comprise high voltage polarization system (9), described body of heater (1) inside arranges upper and lower parallel some heating rods (2); Near described heating rod (2), relative two battery lead plates (4) are set, described battery lead plate (4) is embedded on the surface of described refractory brick, forms thermocouple (5) between two battery lead plates (4); The sample room being made up of two horizontal refractory plates (6) and two vertical refractory brick (7) is set between described two battery lead plates (4); Described battery lead plate (4) is connected with body of heater external high pressure polar system (9) by contact conductor, and described high voltage polarization system (9) is for polarized electric field and the control furnace body temperature of control electrode plate (4).

2. piezoelectric ceramics sintering furnace according to claim 1, is characterized in that, described upper and lower parallel heating rod, and lower heating rod is through refractory brick inside.

3. piezoelectric ceramics sintering furnace according to claim 2, is characterized in that, described upper and lower parallel heating rod, and upper heating rod quantity is 2 times of lower heating rod quantity.

4. piezoelectric ceramics sintering furnace according to claim 1 and 2, is characterized in that, described battery lead plate is the metallic plate of resistance to 1400 DEG C, is coated with the protective layer of silver, gold or platinum on described metallic plate.

5. according to the piezoelectric ceramics sintering furnace described in claim 1-4 any one, it is characterized in that, described refractory slab (6) is alumina high temperature refractory plate.

6. a method of utilizing the piezoelectric ceramics sintering furnace sintering polarization described in claim 1, comprises the following steps:

1) sintering high-temperature poling:

Piezoelectric ceramics sample is put into sintering furnace claimed in claim 1,1100 DEG C-1400 DEG C insulation 2-12 hour, then with 3-8 DEG C at the uniform velocity cool to 1000 DEG C; Naturally cool to afterwards the above 10-20 DEG C of Curie temperature of piezoelectric ceramics, open polarization program, after polarized sample, take out ceramics sample;

2) by electrode:

After piezoelectric ceramics sample takes out, unburned silver slurry is evenly applied to sample upper and lower surface, dries 5-8 minute for 150 DEG C, after silver slurry is dried, can carry out piezoelectric property test.

7. the method for piezoelectric ceramics sintering furnace sintering polarization according to claim 6, it is characterized in that, in described sintering high-temperature poling process, polarization program is for first applying DC electric field 20-40V/mm, and control temperature and decline with 5-10 DEG C/min of speed, increase gradually polarized electric field simultaneously, in the time that furnace temperature drops to 100 DEG C, polarized electric field is increased to 3000V/mm; Naturally be cooled to afterwards room temperature, remove extra electric field, take out ceramics sample.